Parametric seizure detection

ABSTRACT

We report a method for detecting epileptic or non-epileptic seizures, comprising: receiving a heart rate of a patient; calculating a percentage change of the heart rate in reference to at least one of the patient&#39;s maximal heart rate, reserve heart rate, or a resting heart rate; detecting an epileptic seizure if the percentage increase in the heart rate reaches a threshold value; and taking at least one responsive action selected from issuing a warning, delivering a therapy, determining a seizure severity, or logging at least one of a date and time of occurrence of the seizure, its severity, the type of therapy, or its effect, in response to the detection. We also report a medical device system configured to implement the method. We also report a non-transitory computer readable program storage unit encoded with instructions that, when executed by a computer, perform the method.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of and claims priority toU.S. patent application Ser. No. 14/170,389, entitled “ParametricSeizure Detection”, filed on Jan. 31, 2014 which was acontinuation-in-part of U.S. patent application Ser. No. 14/084,513,entitled “Pathological State Detection using Dynamically Determined BodyIndex Range Values”, filed on Nov. 19, 2013. U.S. patent applicationSer. No. 14/170,389 claimed priority to U.S. provisional patentapplications 61/785,429, filed on Mar. 14, 2013; and 61/793,292,61/794,540, and 61/801,950, all filed on Mar. 15, 2013. All of thesepatent applications are hereby incorporated by reference.

FIELD OF THE INVENTION

This disclosure relates to medical device systems and methods capable ofdetecting epileptic seizures.

SUMMARY OF THE INVENTION

In some embodiments, the present disclosure relates to a method fordetecting an epileptic seizure, comprising: receiving a heart rate of apatient; calculating a percentage change of the heart rate in referenceto at least one of the patient's maximal heart rate, a reserve heartrate, an activity heart rate, or a resting heart rate; detecting anepileptic seizure if the percentage increase in the heart rate reaches athreshold value; and taking at least one responsive action selected fromissuing a warning, delivering a therapy, determining a seizure severity,or logging at least one of a date and time of occurrence of the seizure,its severity, the type of therapy, or its effect, in response to thedetection. Other cardiac signals, such as myocardial contractility,ejection fraction, etc., may be applied for detection of brain statechanges such as epileptic seizures.

In other embodiments, the present disclosure relates to a medical devicesystem, comprising one or more components configured to implement partor all of one or more of the steps of the method.

In some embodiments, the present disclosure relates to a non-transitorycomputer readable program storage unit encoded with instructions that,when executed by a computer, perform a method as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be understood by reference to the followingdescription taken in conjunction with the accompanying drawings, inwhich like reference numerals identify like elements, and in which:

FIG. 1 shows a schematic diagram of a medical device system, accordingto some embodiments of the present disclosure;

FIG. 2 shows a schematic diagram of data acquisition elements of amedical device system, according to some embodiments of the presentdisclosure;

FIG. 3 shows a schematic diagram of a patient heart rate module of amedical device system, according to some embodiments of the presentdisclosure;

FIG. 4 shows a flowchart depiction of a method of detecting an epilepticseizure, according to some embodiments of the present disclosure; and

FIG. 5A shows a flowchart for selection of reference heart rates fordetection of epileptic seizure, according to some embodiments of thepresent disclosure.

FIG. 5B shows a flowchart for selection “other reference values”(different from those shown in FIG. 5A) when detection performance usingsaid FIG. 5A values are not satisfactory.

While the disclosure is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and are herein described in detail. It shouldbe understood, however, that the description herein of specificembodiments is not intended to limit the disclosure to the particularforms disclosed, but on the contrary, the intention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the disclosure as defined by the appended claims.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Illustrative embodiments of the disclosure are described herein. Forclarity, not all features of an actual implementation are described. Inthe development of any actual embodiment, numerousimplementation-specific decisions must be made to achievedesign-specific goals, which will vary from one implementation toanother. Such a development effort, while possibly complex andtime-consuming, would nevertheless be a routine undertaking for personsof ordinary skill in the art having the benefit of this disclosure.

More information regarding detecting an epileptic event from cardiacdata, as well as information regarding measures of central tendency thatcan be determined from time series of body data, may be found in otherpatent applications assigned to Flint Hills Scientific, LLC orCyberonics, Inc., such as, U.S. Ser. No. 12/770,562, filed Apr. 29,2010; U.S. Ser. No. 12/771,727, filed Apr. 30, 2010; U.S. Ser. No.12/771,783, filed Apr. 30, 2010; U.S. Ser. No. 12/884,051, filed Sep.16, 2010; U.S. Ser. No. 13/554,367, filed Jul. 20, 2012; U.S. Ser. No.13/554,694, filed Jul. 20, 2012; U.S. Ser. No. 13/559,116, filed Jul.26, 2012; and U.S. Ser. No. 13/598,339, filed Aug. 29, 2012. Each of thepatent applications identified in this paragraph is hereby incorporatedherein by reference.

More information regarding detecting an epileptic event from multiplebody data types, and examples of such body data types, may be found inother patent applications assigned to Flint Hills Scientific, LLC orCyberonics, Inc., such as, U.S. Ser. No. 12/896,525, filed Oct. 1, 2010,now U.S. Pat. No. 8,337,404, issued Dec. 25, 2012; U.S. Ser. No.13/098,262, filed Apr. 29, 2011; U.S. Ser. No. 13/288,886, filed Nov. 3,2011; U.S. Ser. No. 13/554,367, filed Jul. 20, 2012; U.S. Ser. No.13/554,694, filed Jul. 20, 2012; U.S. Ser. No. 13/559,116, filed Jul.26, 2012; and U.S. Ser. No. 13/598,339, filed Aug. 29, 2012. Each of thepatent applications identified in this paragraph is hereby incorporatedherein by reference.

Embodiments of the present disclosure provide for determining apatient's maximal heart rate (MHR), a resting heart rate (RSR), areserve heart rate (RvHR), an activity heart rate (AHR) and a activityreserve heart rate (ARvHR), for use as a reference to detect changes inbrain or body state. The patient's heart rate may be monitored and achange in the heart rate may be detected and measured. If a heart ratechange occurs, the heart rate upon which a detection may be attempted,may be analyzed relative to the at least one of the references MHR, RSR,RvHR, AHR, or ARvHR. If the percentage change of the patient's heartrate, in reference to at least one of the MHR, RSR, RvHR, AHR, or ARvHRis above a threshold change (or in certain cases below it) then anepileptic seizure is deemed to have been detected. Sub-reference heartrate values such as resting heart rate awake (RSRw), heart rate asleep(RSRs) and for sleep, heart rate asleep REM (RSRsrem), heart rate asleepNon-REM (RSRsnrem), reserve heart rate awake (RvHRw) or reserve heartrate asleep (RvHRs), etc., may be used to improve accuracy and speed ofdetection of epileptic seizures and other brain or body state changes.

The magnitude and direction (e.g., increases or decreases) of heartchanges associated with epileptic seizures vary as a function of extentof involvement of the brain by paroxysmal activity (which is generallypartially a function of time) and of certain anatomo-functional factorssuch as location of the epileptogenic network. The location of theepileptogenic network location may have a positive or negativechronotropic effect of variable magnitude. Therefore, ictal heart ratechanges may manifest as increases or decreases in the same patient andmay be small or large. Upon detecting an epileptic seizure, a responseaction may be taken, wherein the responsive action may include issuing awarning, delivering a therapy, determining a seizure severity, orlogging at least one of a data and time of the seizure, its severity,the type of therapy or its effect.

The value (e.g., amplitude, frequency, concentration, rate of change,etc.) of biological (e.g., autonomic, endocrine, metabolic,neurological, etc.) signals from a patient may change as function of oneor more of the state of the patient's health, physical or cognitiveactivity type and levels of the patient, the patient's fitness level,time of day, or the patient's level of consciousness. The statedependency and associated fluctuations (physiological or pathological)of these signals complicates the detection of events, and especiallytheir accurate classification into physiological/desirable orpathological/undesirable. For example, epileptic seizures may increasethe heart rate from 80 bpm to 120 bpm, but a similar change may becaused by exercise, emotions, or certain diseases. While resorting tomultimodal signals (e.g., heart rate, rate of heart change, EKGmorphology, measurement of movement using accelerometers) may in theexample above sort out exertional from epileptic increases in heartrate, a more economical and simpler approach is disclosed herein toclassify or identify changes in biological signals as either desirableor undesirable, and based on their type, take responsive action thatprotects the patient's health and well-being. This approach uses certainreferences (e.g., RSR, MHR, RvHR, etc.) that in the absence of cardiacdisease, generally do not change or may change very slowly and/or byvery small quantities, behaving as parameters in a dynamical sense, acharacteristic that makes them useful as references for detection ofstate changes given their high stationarity. The behavior of theseparameters is fairly stable, unlike the behavior of variables such asinstantaneous heart rate (IHR) and instantaneous respiratory rate,catecholamines levels, etc., that change rapidly and also markedly inresponse to exercise, emotions, cognitive activity or metabolic andendocrine factors, which may change rapidly.

As used herein, a biological signal, such as heart rate, may be avariable (e.g., instantaneous heart rate subject to rapid (e.g., <<1sec) and large (e.g., 80 bpm) variations) or a parameter (e.g., maximalheart rate that does not change or changes very slowly in the absence ofcardiac disease).

The range of fluctuation of autonomic, neurological, endocrine,metabolic, and tissue stress signals are bounded, reaching absolutemaximum (global maximum) or minimum (global minimum) values. Forexample, there is a maximal heart rate defined by the formula 220-age,as well a resting heart rate that remains relatively constant with age.While the different classes of signals listed above have global maximaand global minima, and may be used for detection of undesirable statechanges, it may be desirable to use heart rate due to its ease ofacquisition/recording, its high signal to noise ratio (relative to manyother biological signals), and its ease of computation.

Factors such as age, fitness level, body weight, maximal heart rate,resting heart rate during wakefulness, heart rate during sleep,environmental conditions (conditions external to the patient's body,e.g., temperature, humidity, altitude), etc., are generally not takeninto account for setting thresholds for automated detection ofpathological events in biological time series that are inherentlynon-stationary. For example, state-of-the art automated algorithms forepileptic seizure detection based on heart rate do not take into accountthese parameters, relaying chiefly if not exclusively on variables suchas changes in instantaneous heart rate. As a result, inherent andubiquitous non-ictal fluctuations in those signals are likely to resultin false positive or false negative detections using prior techniques.

Seizure detection performance may be improved in a highlycomputationally efficient manner by using as reference values apatient's one or more parameters and/or normalized values. Examples ofsuch reference values include:

-   1. Maximal heart rate (MHR)—HR which may be calculated using the    formula 220—patient's age or any other valid formula;-   2. Resting heart rate (RHR)—HR as measured during sedentary active    wakefulness or during sleep;-   3. Reserve heart rate (RvHR)—HR which may be calculated as the    difference between the maximal heart rate and the resting heart rate    [e.g., RvHR=MHR (220 bpm-40 years old)—RHR (60 bpm)=120 bpm]; or,-   4. Activity reserve heart rate (ARvHR)—HR which may be calculated as    the difference between the MHR and the current measured heart rate    (CMHR), which will depend on a current activity level or work level    (i.e., a physiological increase in HR).

“Work level” herein refers to the energy consumption of the patient'sbody or a part thereof (e.g., the brain). Energy consumption may, insome embodiments, be measured by differences in oxygen saturation,concentration, or pressure between arterial and venous locations. Insome embodiments of this disclosure, work level may be determined usingmeasures of kinetic activity (force, amplitude, velocity, direction, andduration and rate of muscle contractions) or autonomic activity such asheart rate. “Work level” in this disclosure does not refer exclusivelyto the patient's physical activity. Physical activity may be only one ofmultiple physiological events or states leading to energy consumption bythe patient's body or a part thereof “Work level” may also refer to thephysics definition, W=F×d. The application of force over distance may beonly one of multiple actions by a patient leading to energy consumptionby the patient's body or a part thereof.

Each of these reference values may be further refined to capturedifferent aspects of a patient's body state (e.g., resting heart rateduring non-rapid eye movement (NREM) sleep, Resting heart rate duringREM sleep). Further, the HR rate associated with the current activity orwork level may vary based upon the level of exertion associated with thecurrent activity or work level (i.e., a patient's HR is likely to behigher while jogging than while walking).

The HR resulting from current activity or work level may bephysiological/normal (e.g., exercise) or pathological/abnormal (e.g.,epileptic seizure). Current measured signal value (CMSV) is definedherein generally as the signal value being analyzed to determine whetherthe patient has undergone a change, and whether the change was a resultof physiological or pathological activity. In one embodiment a current(i.e., present time) measured signal value (CMSV) may comprise aninstantaneous value, a median or mean value of a short term time window(e.g., less than thirty seconds). Current measured heart rate (CMHR) isa currently measured signal value resulting from measurement of a signalvalue relative to the heart.

In yet other embodiments, autonomic activity (e.g., respiration,catecholamines), neurologic activity (e.g., kinetic activity thatincludes force of contraction), endocrine activity (e.g., cortisol),metabolic activity (e.g., oxygen consumption) may be used instead of oralong with cardiac activity. In other words, autonomic (e.g., SaO₂),metabolic (arterial pH, lactic acid production and clearance, oxygenconsumption), neurologic (e.g., frequency, velocity, force of musclecontractions, number of body parts involved), tissue stress factors,etc., may be used in a manner similar to cardiac signals. For example,minimal and maximal oxygen consumption, reserve oxygen consumption (thedifference between maximal and current consumption whether duringresting conditions or while engaged in physical activity) may be usedfor detection of certain seizures. Under certain conditions, thereference values of parameters may be pathological but changes in saidvalues may be used for detection of state changes. Any of the bodysignals or indices (e.g., respirations, body movements, etc.) may beused to validate and verify detection performance based on another bodysignal. For example, detections using heart rate may be validated usingbody movements (e.g., kinetic signals). False positive or false negativedetections may be identified by comparing changes in a body signal valuewith a different body signal, to improve detection performance andclinical usefulness.

Ratios or other mathematical expressions between theseparameters/variables may be used instead of their differences.

One of the advantages of the approach disclosed herein compared to thepresent state of the art that requires the continual collection andcalculation of a foreground and background value. By way of an exampleof a present state of the art methodology, HR is used to compute aforeground/background value that is then analyzed relative to variousdetection thresholds. In contrast, in the present approach, continualbackground/foreground updating is unnecessary since MHR, RHR are knownand highly stable. Typically MHR and RHR change by no more than 1bpm/year under normal circumstances. Another noteworthy advantage to thepresent approach is the data normalization inherent to this approach fora patient's physiological traits (e.g., the patient's age, fitness leveland current heart or respiratory rate values). While only heart andrespiratory signals have been mentioned herein, other autonomic,endocrine, neurologic, metabolic or body stress marker signals may beapplied for seizure detection.

EXAMPLE 1

Patient is 40 years old. MHR=180 bpm; RHR 60 bpm; RvHR: 120 bpm. Anevent is occurring that increases the patient's heart rate to a currentmeasured value (CMHR) of 155 bpm. If a seizure occurs when this patientis resting, the large difference between the RHR and the CMHR (e.g.,Current measured value (CMHR)(155 bpm)−RHR (60 bpm)=+95 bpm) stronglysuggests that the change in heart rate is indicative of a seizure, andthat the probability of a false positive or false negative detection islow. However, if the patient was exercising instead of resting justprior to the time of seizure onset, with a prior measured heart rate(PMHR) at 140 bpm, (corresponding to an ARvHR of 40 bpm), the detectionmargin is a much smaller +15 bpm (e.g., Current measured value (155bpm)−PMHR (140 bpm) =+15 bpm), and the smallness of this marginincreases the probability of a false negative detection unless someadaptation is made. However such an adaptation (e.g., reduction of thedetection threshold) would increase the probability of a false positivedetections at other times/circumstances unless the adaptation were“intelligent” since sensitivity and specificity of detection competewith each other (i.e., one of these variables cannot be optimizedwithout degrading the other).

One of the most commonly used event detection strategies is to parse thedata into two segments, one containing the most contemporaneous data(e.g., foreground) and the other, older data that serves as reference(e.g., background) against which changes in the foreground aredetermined. The choice of certain parameters such as length of thebackground/reference segment and the rate at which it is updated, ismade to reduce its innate variability and minimize the negative impactit may have on the performance (sensitivity specificity and speed ofevent detection) of the detection algorithm. The steps taken to reducepotentially large fluctuations in the value(s) of thereference/background segment, are only partially successful inminimizing detection performance “glitches” since the degree ofreduction in non-stationarity/variability that would be required toreduce the task of event detection from a “two-variable problem” (thatloosely speaking may be labeled as “pseudo-intractable”) to aone-variable (tractable) problem will markedly degrade its information(dynamical) content to the detriment of detection performance. Thisinvention makes the detection problem highly tractable (while optimizingdetection performance) by selecting reference values (e.g., MHR, RHR)that while highly representative/informative of the dynamics of thesystem under study, are not subject to wide or rapid fluctuations, thusbehaving as parameters in a dynamical sense. In short, this inventionreduces a “2-variable” problem into a 1-variable without sacrificingdynamical information. The 2-variable event detection problem posed bythe foreground/background approach in non-stationary (EEG, EKG)time-series is more complex than the one in algebra since the variablesin the case of the time series used for seizure detection arenon-stationary (i.e., continuously varying). Methodologies dependentupon foreground and background time window-based heart rates, both ofwhich are non-stationary (the 2-variables problem) are associated with ahigher probability of false positive and false negative detections thanwould those with only one variable (e.g., foreground).

Returning to Example 1, if the heart rate just prior to the time ofseizure onset is 60 bpm (e.g., the patient is asleep), almost anythreshold value (e.g., an absolute number of beats, such as +15 bpm or+30 bpm, or a percentage value, such as +25%) may be applied withoutadversely impacting sensitivity of detection. If speed of detection ishighly important for therapeutic efficacy and to avoid injuries viaearly warning, low increases (e.g., +15 bpm or even a smaller (<+15 bpm)increase may serve this purpose even better. By contrast, if the heartrate just prior to the time of seizure onset is 140 bpm, leaving adetection margin of only +15 bpm, the probability of a false negativedetection would increase. However, if the patient's resting heart valueduring wakefulness or sleep is selected as a reference value (i.e., afiducial) the resultant increase in the detection margin (from +15 to aminimum of +70 bpm and to as much as +95 bpm) would improve detectionperformance under certain circumstances or conditions (where sensitivityand speed of detection are paramount for patient safety or therapeuticefficacy) by decreasing the probability of false negative detections. Apreviously measured heart rate (PMHR) (e.g., 140 bpm) to reference value(e.g., RHR=60 bpm) dimensionless ratio (140/60=2.3) may be alsocalculated. Any increases in the ratio above a threshold value (e.g.,2.3), as would be the case if the rate increased from 140 bpm to 155 bpm(155/60=2.6), would trigger a seizure detection and other actions, suchas therapy delivery.

While the positive (+) sign has been used in describing these concepts,the present invention contemplates the use of routine mathematicaltransformations that would yield comparable results, e.g., subtractinglarger positive numbers from smaller positive numbers to yield negativevalues having the same absolute value as the reverse subtraction, i.e.,|75 bpm−60 bpm|=|60 bpm−75 bpm|, or quantifying an increase as apercentage relative to a baseline instead of an absolute number of beatsper minute, among other mathematical operations known to the person ofordinary skill in the art. It should be noted that epileptic seizuresmay also cause bradycardia, although with a prevalence much lower thantachycardia. Regardless, the approaches (with appropriate modifications)in this disclosure may be applied to both cases.

The choice of reference value (e.g., MHR v. RHR v. RvHR v. ARvHR) uponwhich detections is based may depend on the state of the patient (e.g.,awake v. asleep; resting v. in motion, etc.), which is correlated (inotherwise healthy epileptics) with heart rate values (i.e., low (e.g.,60-70 bpm) heart rate values indicate an adult subject is resting,intermediate values (e.g., 80-90 bpm) a moderately physically activesubject and higher values (e.g., 110-140 bpm) an indicator that thesubject may be jogging), by extension on the Current Measured HR, and/orthe performance (false positive, false negative, positive predictivevalue, speed of detection, etc.) required of a detection method tomaximize patient safety and therapeutic efficacy. For example, when apatient is asleep or resting, the heart rate is near its global minima,so that the probability of false seizure detections based on changes inthe Current Measured heart rate (CMHR) (e.g., HR in sleep is 60 bpm(RHR) and suddenly jumps to 90 bpm, which would equal an increase of33%) if used as the reference value, is likely to be higher compared toa detection using as a reference value the heart rate while the patientis exercising or one of the RHR or ARvHR. In this example (patientasleep with low heart rate), MHR may be the preferred reference value.However, if the patient is exercising and the CMHR is 140 just prior tothe time of seizure onset, the issuance of detection will take longerthan at a lower CMHR, while the probability of not detecting the seizurewill also be higher (vis-a-vis a lower CMHR), especially if the heartrate change increase caused by a seizure (i.e., a pathological changeequal to +15 bpm in this case) is modest; basing the detection on apercentage change of the resting heart rate (RHR) will increase theprobability of detecting the seizure. In general, the lower the CMHR,the more the MHR would be the preferred reference choice, while forhigher CMHR, the RHR may be the preferred reference for detection ofseizures. In one embodiment, the increase in heart rate above an CMHRcaused by a seizure (SzHR) may be used as the preferred reference fordetection purposes and in another embodiment, the increase in heart ratecaused by activity (other than seizures) above a resting value may beused as a reference value.

As used herein, when a value is said to be “near” a reference value, itmay have a percentage value within, e.g., ±10% of the reference value,and/or a percentile value placing it within, e.g., the decile, thequartile, or the like of the value's distribution closest to thereference value.

The case when seizures occur during transitions from one state toanother state (e.g., as from sleep to wakefulness, wakefulness to sleepphysical activity to physical inactivity, or physical inactivity tophysical activity) may require a different approach than the onepreviously outlined. Since state transitions are typically accompaniedby changes in heart rate (increase or decreases), independent of thosecaused by epileptic seizures or other pathological events, accuratedetection of undesirable events may be limited by the temporal overlapof non-epileptic and epileptic changes. One of several possiblestrategies to address this is to “fix” the prevailing Current Measuredheart rate (CMHR) for a certain time period (e.g., 2 min) so that ifseizures occur during state transition that are associated with large(or confounding for detection purposes) non-epileptic changes in heartrate, detection performance will not be degraded. The length of thewindow for fixation of a variable may be optimized based on historicaldata and optimized on- or, off-line. The process of adaptation andoptimization may be iterative and encompass not only the case alluded toin this paragraph but also seizure detection within a state.

These reference values (e.g., MHR, RHR, RvHR, ARvHR may be put intovarious formulae or equations to determine, in a more reliable manner,which increases (or decreases) in heart rate are indicative of theoccurrence of an epileptic seizures. In a particular embodiment, one ormore of the reference and/or subreference values described herein may beused to partially or wholly distinguish epileptic seizures fromnon-epileptic seizures. More information on distinguishing epilepticseizures from non-epileptic seizures is provided in U.S. Ser. No.13/288,886, filed Nov. 3, 2011, which is hereby incorporated herein byreference.

In one embodiment, one or more of the reference and/or subreferencevalues described herein may be used to determine a confidence index forthe sensitivity and/or specificity of detections.

FIG. 1 shows a schematic diagram of a medical device system 200,according to some embodiments of the present disclosure. The medicaldevice system 100 may comprise a medical device 200, sensor(s) 212, andlead(s) 211 coupling the sensor(s) 212 to the medical device 200. Thesensor(s) 212 may be configured to collect one or more body signals froma patient, such as autonomic, kinetic, or other body signals. In oneembodiment, the at least one sensor 212 is configured to collect atleast one cardiac signal.

Various components of the medical device 200, such as controller 210,processor 215, memory 217, power supply 230, communication unit 240,warning unit 192, therapy unit 194, logging unit 196, and severity unit198 have been described in other patent applications assigned to FlintHills Scientific, LLC or Cyberonics, Inc., such as those incorporated byreference, supra. In one embodiment, the medical device 200 may comprisea body data module 150 configured to receive a heart rate value of thepatient, based at least in part on the cardiac signal, and optionallyalso on an environmental conditions unit 172 providing, for example,information about temperature, humidity, altitude, luminance, ambientloudness, and/or electro-magnetic noise, among others.

The medical device 200 may comprise a body data change module 160configured to calculate a percentage change of the heart rate inreference to at least one of the patient's maximal heart rate, reserveheart rate, or a resting heart rate. Other functions, such as choosingthe signal type (autonomic and/or kinetic, among others) and/or thenumber of signals (one or more), may be performed by medical device 200.

In some embodiments, the body data change module 160 may be configuredto select the resting heart rate (RHR) from at least one of a non-REMsleep heart rate (RSRsnrem), a REM sleep heart rate (RSRsrem), animmediately upon awakening in a recumbent position resting heart rate,an immediately upon awakening in a sitting position resting heart rate,an immediately upon awakening standing still resting heart rate, asometime after awakening standing still resting heart rate, a sometimeafter awakening in a recumbent position resting heart rate, a sometimeafter awakening in a sitting position resting heart rate, a restingheart rate after having completed a physical activity, a resting heartrate awake (RSRw), a heart rate asleep (RSRs).

In some embodiments, the body data change module 160 may be configuredto determine the reserve heart rate is one of the difference between thepatient's maximal heart rate and a resting heart rate, or the differencebetween the maximal heart rate and an activity heart rate.

The medical device 200 may comprise a patient heart rate (HR) module180. The patient HR module 180 may be configured to provide the valuesof the MHR, RHR, RvHR, AHR, and the ARvHR. In one embodiment, the valuesof the MHR, RHR, RvHR, ARvHR, and the AHR may be stored in the patientHR module 180, wherein in other embodiments, these values may becalculated, and/or updated by the patient HR module 180.

In some embodiments, the body data change module 160 may be configuredto select the maximal heart rate, the reserve heart rate, the reserveactivity heart rate, the activity heart rate, or the resting heart ratebased on at least one of an instantaneous heart rate value, a time ofday, a state of the patient (e.g., awake v. asleep), a change in apatient health status, a change in fitness level, a change in bodyweight, a change in body mass index, or at least on changes inmedications (with cardiovascular effects) prescribed to the patient.

Alternatively or in addition, the medical device 200 may comprise athreshold modification module (not shown). The threshold modificationmodule may be configured to modify the threshold value based on at leastone of a time of day, a state of the patient, a patient health status,at least one environmental condition, or at least one medicationprescribed to the patient.

The embodiment shown in FIG. 1 shows various modules, such as body datamodule 150, body data change module 160, and patient HR module 180, asseparate modules. In other embodiments (not shown), one or more ofmodules 150, 160, or 180 may be a component of another of modules 150,160, or 180 and/or another module of medical device 200. For example, inone embodiment (not shown), patient HR module 180 may be a component ofbody data change module 160.

The medical device 200 may comprise a seizure detection module 170configured to detect an epileptic seizure if the percentage increase inthe heart rate reaches a threshold value.

The medical device 200 may comprise at least one additional moduleselected from a warning unit 192 configured to issue a warning of theseizure, a therapy unit 194 configured to deliver a therapy for theseizure, an adverse effect unit 174 configured to determine the presenceof and optionally, if present, assess an adverse effect of the therapy,a severity unit 198 configured to determine a seizure severity, or alogging unit 196 configured to log at least one of a date and time ofoccurrence of the seizure, its severity, the type of therapy, or itseffect.

FIG. 2 shows a schematic representation of components of the medicaldevice system, particularly, body data module 150 of medical device 200,as well as an autonomic data acquisition unit 260, a neurological dataacquisition unit 270, an endocrine data acquisition unit 273, ametabolic data acquisition unit 274, and a tissue stress marker dataacquisition unit 275. More information regarding multiple body datatypes, data collection thereof, and use thereof in epileptic eventdetection may be found in other patent applications assigned to FlintHills Scientific, LLC or Cyberonics, Inc., such as, U.S. Ser. No.12/896,525, filed Oct. 1, 2010, now U.S. Pat. No. 8,337,404, issued Dec.25, 2012; U.S. Ser. No. 13/098,262, filed Apr. 29, 2011; U.S. Ser. No.13/288,886, filed Nov. 3, 2011; U.S. Ser. No. 13/554,367, filed Jul. 20,2012; U.S. Ser. No. 13/554,694, filed Jul. 20, 2012; U.S. Ser. No.13/559,116, filed Jul. 26, 2012; and U.S. Ser. No. 13/598,339, filedAug. 29, 2012. Each of the patent applications identified in thisparagraph is hereby incorporated herein by reference.

The body data module 150 may also comprise a force sensing unit 291configured to determine an amount of force generated by part or all of apatient's body, which may provide an indication of the patient'sactivities.

The body data module 150 may also comprise a blood gases acquisitionunit 265. In some embodiments, blood gases acquisition unit 265 may beconfigured to detect blood oxygen saturation at one or more points in apatient's carotid artery, jugular vein, superior vena cava, inferiorvena cava, or a left ventricle of the heart. In alternative embodiments,blood gases acquisition unit 265 may be configured to detect bloodoxygen saturation in additional blood vessels and/or organ target sitesof the patient's body. In some embodiments, blood gases unit 265 maycomprise an arterio-venous oxygen difference determination unit 2741configured to determine an arterio-venous oxygen difference, and anoxygen consumption determination unit 2742 configured to determine anoxygen consumption from the arterio-venous oxygen difference. In yetother embodiments, CO₂ pressures or concentrations may be measured.

Turning now to FIG. 3, a stylized block diagram depiction of the patientHR module 180, in accordance with one embodiment, is illustrated. Thepatient HR module 180 comprises a patient data unit 310, a cardiac dataunit 320, a patient activity unit 330, and a patient HR-reference unit340. The patient data unit 310 may receive body data, as well as generaldata about the patient. For example, the patient's age, general health,fitness level, specific health issues, medication regimens, etc., may bestored in the patient data unit. These data may be used by the cardiacdata unit 320 to determine relevant heart data that could impact thevalues of the MHR, RHR, RvHR, PMHR, and the ARvHR. Further the patientactivity unit 330 may comprise data relating the patient's activitylevel, current activities, and/or historical activities. Data from thecardiac data unit 320 and the patient activity unit 330 may be used bythe patient HR-reference unit 340 to select a parameter reference fromone of MHR, RHR, RvHR, and/or the ARvHR, based on the heart rate at thetime of a change in the present/current heart rate, or more specificallyon the heart rate immediately prior to the onset of a seizure (CMHR).(“Present/current heart rate” encompasses, but is not limited to, aninstantaneous heart rate). While emphasis has been placed on epilepticseizure detection, non-epileptic seizure detection is feasible usingthis invention, given the quantitative differences in changes in variousbody signals between epileptic and non-epileptic seizures. For example,changes in autonomic, metabolic, endocrine, neurologic, and/or tissuestress signals may be more pronounced and/or longer-lasting withepileptic than non-epileptic seizures.

In some embodiments, the present disclosure relates to a method fordetecting an epileptic seizure, comprising receiving a heart rate of apatient; calculating a percentage change of the heart rate in referenceto at least one of the patient's maximal heart rate (MHR), reserve heartrate (RvHR), activity reserve heart rate (ARvHR), or a resting heartrate (RHR); detecting an epileptic seizure if the percentage increase inthe heart rate reaches a threshold value; and, taking at least oneresponsive action selected from issuing a warning, delivering a therapy,determining a seizure severity, or logging at least one of a date andtime of occurrence of the seizure, its severity, the type of therapy, orits effect, in response to the detection.

The resting heart rate (RHR) may be selected from one of an NREM sleepresting heart rate, a REM sleep resting heart rate, an immediately uponawakening in a recumbent position resting heart rate; an immediatelyupon awakening in a sitting position resting heart rate, an immediatelyupon awakening standing still resting heart rate; a sometime afterawakening standing still resting heart rate, a sometime after awakeningin a recumbent position resting heart rate, a sometime after awakeningin a sitting position resting heart rate, or a sometime after havingcompleted a physical activity resting heart rate.

The reserve heart rate may be selected from one of the differencebetween the patient's maximal heart rate and a resting heart rate(RvHR), or the difference between the maximal heart rate and an activityheart rate (ARvHR).

The maximal heart rate, the reserve heart rate, or the resting heartrate may be selected based on at least one of an instantaneous heartrate value, a time of day, a state of the patient, a patient healthstatus, a fitness level, environmental conditions, or at least onemedication prescribed to the patient.

In some embodiments, the method may further comprise modifying thethreshold value based on at least one of a time of day, a state of thepatient, a patient health status, a fitness level, environmentalconditions, or at least one medication prescribed to the patient. Thethreshold value may be modified while being based on an unchangedreference value.

Turning now to FIG. 4, a method 400 for performing a seizure detection,in accordance with an embodiment of the present disclosure, isillustrated. A heart rate signal may be acquired (at 410), for examplein a moving time window. The heart rate signal may be processed andanalyzed (at 420) to yield current measured heart rate (CMHR). Inresponse (at 430) to a determination that said CMHR has changed or isabove a threshold change, a HR-reference selection process may beperformed (at 440), to select an MHR, a RvHR, a ARvHR or an RHR. A moredetailed description of the HR-reference selection process is providedin FIGS. 5A and 5 b and the accompanying description below.

Upon performing an HR-reference selection, the HR-reference value iscompared and/or related to the CMHR (at 450). If the CMHR does notdiffer from the HR-reference by a threshold percentage (at 460), noseizure is declared (at 465). However, if the CMHR differs from theHR-reference by the threshold percentage (at 460), a seizure event isdeclared (at 470). Further, a responsive action may be taken (at 480),which may include issuing a warning, delivering a therapy, determining aseizure severity, or logging at least one of a data and time of theseizure, its severity, the type of therapy or its effect.

FIG. 5A and FIG. 5B depict a process of selecting the HR-reference.Examples of this HR-reference may include the MHR, RvHR, ARvHR or anRHR. A patient's heart rate may be determined using any appropriatetechnique and apparatus described above, included in a patentapplication incorporated herein by reference, or known to the person ofordinary skill in the art.

Alternatively or in addition to RHR, MHR, AHR, RvHR, and ARvHR, in oneembodiment, other reference values may be derived from two or more ofthese values in any permutations and/or mathematical transformation(e.g., average value, ratios, etc . . . ). Which HR-reference value(s)are to be selected may depend upon the current measured heart rate(CMHR) and its relative position related to either a minimal heart rate(e.g., RHR) or a maximum heart rate value (e.g., MHR). For example, therange of possible CMHR values spans between RHR and MHR. Inside thisrange is a mean, a median, or some other measure of central tendency.For a CMHR value between RHR and the measure of central tendency, theRHR may be selected as an initial HR-reference value upon which thepermutation or other transformation may be based. For a CMHR valuebetween the measure of central tendency and MHR, the MHR may be selectedas the HR-reference value upon which the permutation or othertransformation may be based.

This approach may reduce the search space and facilitate decision makingin a computational cost effective way.

FIG. 5A depicts a flowchart representation of one method of selectingthe HR-reference. If the patient's CMHR is determined to be at or near aresting level (at 510), then the patient's maximal heart rate may beused as the reference value (at 515). However, if the patient's heartrate is not near a resting level, then the method may comprisedetermining if the patient's CMHR is near the maximal level (at 520).

If the patient's CMHR is determined to be near the maximal level (at520), then a resting heart rate (RHR) of the patient may be used as thereference value (at 525).

If the patient's heart rate is not near the maximal level, then themethod may comprise determining if the patient's heart rate is betweenthe mean or median value and the resting level (at 530). If thepatient's CMHR falls within this range, then the patient's reserve heartrate (RvHR) may be used as the reference value (at 535).

If the patient's heart rate falls within the range of values between themean or median and the maximal value (at 540), the patient's activityreserve heart rate (ARvHR) may be used as the reference value (at 545).If not, another reference value may be used (at 547).

As should be apparent to the person of ordinary skill in the art, inother embodiments, the HR reference may be selected from any one or moreof MHR, RHR, RvHR, AHR, or ARvHR, and the candidate reference values maybe examined in any order, i.e., not necessarily in an order that may beimplied by FIG. 5A.

Turning to FIG. 5B, in some embodiments, once a HR-reference value isselected, a determination may be made whether the selected HR-referencevalue provides the desired sensitivity, specificity and speed of seizuredetection. The determination as to whether the HR-reference performed tothe desired levels may be based upon manual observation, secondaryanalysis, etc. If the determination were made that the selected HRreference is satisfactory, the patient's heart rate may be measured andcompared to identified threshold values. However, if the determinationwere that the system response is unsatisfactory, other reference valuescan be identified and used. The quality of the performance (e.g,satisfactory, unsatisfactory) may be based on the number of falsepositive and/or false negative detections, and/or the speed ofdetection, for a reference value. Alternatively or in addition, in someembodiments, the positive predictive value may be used to assess theperformance. False positive and false negative detections may bedetermined through validation/invalidation of a detection, oridentification of a missed detection, using at least one differentfeature of the same body signal, at least one feature of a differentbody signal, visual expert or expert system analysis of the time seriesof the same or different body signal (on- or off-line), or two or morethereof

FIG. 5B further elaborates on the end steps. At step 550, adetermination is made whether or not detection performance issatisfactory. If the detection is satisfactory, then the process of FIG.5A is repeated (at 555). However, if the determination is made thatdetection performance is unsatisfactory, a different reference value isselected (at 560). Once this different reference value is selected,another determination is made as to whether or not detection performanceis satisfactory (at 570). If the detection performance isunsatisfactory, then the process repeats step 560. If the detection issatisfactory, then the detection algorithm continues to utilize theidentified reference value (at 580).

By way of example, the process of adjusting automated seizure detectionsmay be performed based on utilization of a percentage change in at leastone of the: 1. maximal heart rate (MHR); 2. resting heart rate (RHR); 3.reserve heart rate (RvHR); or, 4. Activity reserve heart rate (ARvHR).

Taking the heart rate values of Example 1 above: MHR: 180 bpm; RHR: 60bpm; RvHR: 120 bpm; PMHR: 140 bpm (indicating exercise); ARvHR: 40 bpm;Current Measured heart rate (CMHR): 155 bpm. The choice of referencevalue may be made based on the prevailing patient conditions, safetyrisks, or circumstances. For example, if a patient has partial seizureswith secondary generalization (invariably associated with falls to theground) that are abated if therapy is delivered within 5 sec ofelectrographic onset (while the patient is still aware and responsiveand the patient is running), sensitivity and speed of detection must bemaximized to minimize the probability of serious injuries should thepatient have a seizure. In this case, an ARvHR (40 bpm) may be chosen asa reference to compute a ratio (140/40=3.5) that serves as a detectionthreshold. Any ratio values above 3.5 (as it would be the case when HRincrease to 155 bpm: 155/40=3.9) such as 3.6 will trigger an earlydetection and therapy delivery likely to abate the seizure, thusprotecting the patient from injuries. On the other hand, if a patientwith partial seizures with secondary generalization is lying in bed andthe anti-seizure therapy is efficacious but associated with intolerableside effects, specificity, not sensitivity or speed of detection, isparamount. In this case, the RvHR may be chosen to compute a ratio or tocalculate a percentage or non-percentage increase in heart rate before adetection and other actions are taken in response to the seizure.

In a different case of Example 1, a detection may be issued if and whenthe current measured heart rate (CMHR) is one of: 22.2% of the MHR abovethe previously measured heart rate PMHR value; 33.3% of the RvHR abovethe PMHR value, or 66.7% of the RHR above the PMHR value. This is a formof detection “normalization” as the increase in bpm required to issue adetection in each alternative is the same (+40 bpm).

In one embodiment, the choice of heart rate reference value for a givenpatient in a given condition, state, safety risk, efficacy and sideeffects of a therapy, may be made based on the best trade-off betweenfalse negative and positive detections using for example receiveroperating curves or some other optimization method.

The method depicted in FIGS. 5A and 5B may allow the detection of anepileptic event with improved sensitivity relative to prior methods. Thesequence in which identified HR reference values are identified may beperformed in various sequential or non-sequential orders.

The methods depicted in FIGS. 4-5B and/or described above may begoverned by instructions that are stored in a non-transitory computerreadable storage medium and that are executed by, e.g., a processor 217of the medical device 200. Each of the operations shown in FIGS. 4-5Band/or described above may correspond to instructions stored in anon-transitory computer memory or computer readable storage medium. Invarious embodiments, the non-transitory computer readable storage mediumincludes a magnetic or optical disk storage device, solid state storagedevices such as flash memory, or other non-volatile memory device ordevices. The computer readable instructions stored on the non-transitorycomputer readable storage medium may be in source code, assemblylanguage code, object code, or other instruction format that isinterpreted and/or executable by one or more processors.

In some embodiments, the present disclosure may provide the followingnumbered paragraph(s):

A non-transitory computer readable program storage unit encoded withinstructions that, when executed by a computer, perform a method fordetecting a seizure, comprising: receiving a current measured heart rate(CMHR) of a patient; receiving at least one heart rate reference(HR-reference) selected from said patient's maximal heart rate, areserve heart rate, an activity heart rate, or a resting heart rate; anddetecting a seizure based on said CMHR and said HR-reference.

What is claimed:
 1. A non-transitory computer readable program storageunit encoded with instructions that, when executed by a medical device,perform a method for detecting an epileptic seizure, comprising:receiving a heart rate of a patient; determining via one or moreprocessors if there is a change in the heart rate; in response todetermining there is the change in the heart rate, calculating via theone or more processors a percentage change of the heart rate inreference to at least one of the patient's maximal heart rate, a reserveheart rate, an activity heart rate, or a resting heart rate; detectingvia the one or more processors the epileptic seizure if the percentagechange in the heart rate reaches a threshold value; and, in response tothe detection of the epileptic seizure taking a responsive actionselected from one of: issuing a warning; delivering a therapy;determining a seizure severity; and logging one of a date and a time ofoccurrence of the epileptic seizure, an epileptic seizure severity, atype of therapy and a therapy effect.
 2. The non-transitory computerreadable program storage unit of claim 1, wherein the change isexpressed as a percentile value change.
 3. The non-transitory computerreadable program storage unit of claim 1, wherein the resting heart rateis selected from at least one of a non-REM sleep heart rate (RSRsnrem),a REM sleep heart rate (RSRsrem), an immediately upon awakening in arecumbent position resting heart rate, an immediately upon awakening ina sitting position resting heart rate, an immediately upon awakeningstanding still resting heart rate, a sometime after awakening standingstill resting heart rate, a sometime after awakening in a recumbentposition resting heart rate, a sometime after awakening in a sittingposition resting heart rate, a resting heart rate after having completeda physical activity, a resting heart rate awake (RSRw), or a restingheart rate asleep (RSRs).
 4. The non-transitory computer readableprogram storage unit of claim 1, wherein the reserve heart rate is oneof a first difference between the patient's maximal heart rate and theresting heart rate, or second difference between the maximal heart rateand the activity heart rate.
 5. The non-transitory computer readableprogram storage unit of claim 1, wherein the method further comprisesselecting at least one of the maximal heart rate, the reserve heartrate, the activity heart rate, or the resting heart rate based on atleast one of an instantaneous heart rate value, a time of day, a stateof the patient, a patient health status, a patient fitness level, atleast one environmental condition, or at least one medication prescribedto the patient.
 6. The non-transitory computer readable program storageunit of claim 1, wherein the method further comprises modifying thethreshold value for seizure detection based on at least one of a time ofday, a state of the patient, a patient health status, a patient fitnesslevel, at least one environmental condition, a patient emotional status,or at least one medication prescribed to the patient.
 7. A medicaldevice system, comprising: at least one sensor configured to collect atleast one cardiac signal from a patient; and a medical device,comprising: a body data module configured to receive a heart rate valueof the patient, based at least in part on the cardiac signal; a patientheart rate module to provide at least one of a patient's maximal heartrate, a reserve heart rate, or a resting heart rate and to calculate achange of the heart rate in reference to at least one of the patient'smaximal heart rate, the reserve heart rate, an activity heart rate, orthe resting heart rate; a seizure detection module configured to detectan epileptic seizure if the change in the heart rate reaches a thresholdvalue; and, at least one additional module selected from a warning unitconfigured to issue a warning of the epileptic seizure, a therapy unitconfigured to deliver a therapy for the epileptic seizure, a severityunit configured to determine an epileptic seizure severity, or a loggingunit configured to log at least one of a date and a time of occurrenceof the epileptic seizure, an epileptic seizure severity, a type oftherapy, or a therapy effect.
 8. The medical device system of claim 7,wherein the patient heart rate module comprises: a patient data unit toprovide at least one of patient body data selected from a groupconsisting of a patient's age, a body weight, a body mass index, ahealth condition, a fitness level, medication regimens, an autonomicdata, a neurological data, an endocrine data, a metabolic data, and atissue stress marker data; a patient activity unit to provide datarelating to a patient's activity level; and a patient HR-reference unitto provide at least one of the maximal heart rate (MHR), the restingheart rate (RHR), the reserve heart rate (RvHR), the activity heart rate(AHR), or the reserve activity heart rate (RAHR) based upon data from atleast one of the patient data unit, the cardiac data unit, or thepatient activity unit.
 9. The medical device system of claim 7, whereinthe body data change module is configured to select the resting heartrate from at least one of a non-REM sleep heart rate (RSRsnrem), a REMsleep heart rate (RSRsrem), an immediately upon awakening in a recumbentposition resting heart rate, an immediately upon awakening in a sittingposition resting heart rate, an immediately upon awakening standingstill resting heart rate, a sometime after awakening standing stillresting heart rate, a sometime after awakening in a recumbent positionresting heart rate, a sometime after awakening in a sitting positionresting heart rate, a resting heart rate after having completed aphysical activity, a resting heart rate awake (RSRw), or a heart rateasleep (RSRs).
 10. The medical device system of claim 7, wherein thebody data change module is configured to determine the reserve heartrate as a first difference between the patient's maximal heart rate andthe resting heart rate, or a second difference between the maximal heartrate and the activity heart rate.
 11. The medical device system of claim7, wherein the body data change module is further configured to selectthe maximal heart rate, the reserve heart rate, the activity heart rate,or the resting heart rate based on at least one of an instantaneousheart rate value, a time of day, a state of the patient, a patienthealth status, at least one environmental condition, or at least onemedication prescribed to the patient.
 12. The medical device system ofclaim 7, further comprising a threshold modification module configuredto modify the seizure detection threshold value based on at least one ofa time of day, a state of the patient, a patient health status, apatient emotional status, at least one environmental condition, or atleast one medication prescribed to the patient.
 13. The medical devicesystem of claim 7, further comprising at least one sensor configured tocollect body data relating to one or more of a patient's autonomic data,a neurological data, an endocrine data, a metabolic data, and a tissuestress marker data.
 14. The medical device system of claim 7, whereinthe patient heart rate module further comprises an environmental unit toprovide data relating to at least one of a temperature, a humidity, analtitude, a luminance, an ambient loudness, or an electro-magneticnoise.
 15. A non-transitory computer readable program storage unitencoded with instructions that, when executed by a medical device,perform a method for detecting a seizure, comprising: receiving a heartrate of a patient; calculating via one or more processors a change inthe heart rate in reference to at least one of the patient's maximalheart rate, a reserve heart rate, an activity heart rate, or a restingheart rate; detecting the seizure if the change in the heart ratereaches a threshold value; and taking at least one responsive actionselected from issuing a warning, delivering a therapy, determining aseizure severity, or logging at least one of a date and time ofoccurrence of the seizure, a seizure severity, a type of therapy, or atherapy effect, in response to the detection.
 16. The non-transitorycomputer readable program storage unit of claim 15, wherein the seizureis an epileptic or a non-epileptic seizure.
 17. The non-transitorycomputer readable program storage unit of claim 15, wherein the changeis a percentage change or percentile change.
 18. The non-transitorycomputer readable program storage unit of claim 15, wherein the restingheart rate is selected from at least one of a non-REM sleep heart rate(RSRsnrem), a REM sleep heart rate (RSRsrem), an immediately uponawakening in a recumbent position resting heart rate, an immediatelyupon awakening in a sitting position resting heart rate, an immediatelyupon awakening standing still resting heart rate, a sometime afterawakening standing still resting heart rate, a sometime after awakeningin a recumbent position resting heart rate, a sometime after awakeningin a sitting position resting heart rate, a resting heart rate afterhaving completed a physical activity, a resting heart rate awake (RSRw),or a resting heart rate asleep (RSRs).
 19. The non-transitory computerreadable program storage unit of claim 15, wherein the reserve heartrate is one of a first difference between the patient's maximal heartrate and the resting heart rate, or a second difference between themaximal heart rate and the activity heart rate.
 20. The non-transitorycomputer readable program storage unit of claim 15, wherein the methodfurther comprises selecting at least one of the maximal heart rate, thereserve heart rate, the activity heart rate, or the resting heart ratebased on at least one of an instantaneous heart rate value, a time ofday, a state of the patient, a patient health status, a patientemotional status, a patient fitness level, at least one environmentalcondition, or at least one medication prescribed to the patient.
 21. Thenon-transitory computer readable program storage unit of claim 15,wherein the method further comprises modifying the threshold value basedon at least one of a time of day, a state of the patient, a patienthealth status, a patient fitness level, at least one environmentalcondition, or at least one medication prescribed to the patient.